Features

Rain Check

Under a consent order to minimize untreated wastewater discharges during wet weather events, the Columbus, Ohio, Division of Sewerage and Drainage evaluated treatment processes that could handle intermittent high-volume, low-strength flows. After reviewing several alternatives, the city decided to pilot-test two promising high-rate clarification systems. Both use ballasted flocculation to treat wet weather flows. Read full article.

Tunneling a Solution

Storage tunnels keep overflows at bay

John Trypus, David Egger, Donnie Ginn, Cary Hirner, and Gary Hunter

Wet weather events can fill combined and sanitary sewers to capacity, discharging a mixture of stormwater runoff and sewage directly into waterways. Today, many cities are challenged to control combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs) and build abatement facilities to improve water quality.

In seeking a solution, municipalities need abatement measures that will significantly reduce and eventually eliminate the volume and frequency of overflows. One option is constructing consolidation pipelines to divert CSOs and SSOs to a storage and conveyance tunnel. Overflows then can be stored until the wet weather event subsides, when excess flows are conveyed to wastewater treatment plants.

The most successful storage tunnel projects merge an integrated operation and monitoring strategy with heavy civil engineering design expertise. Project engineers must take into account a broad variety of important hydraulic, water quality, design, construction, and operating factors. Read full article.

Cutting Through the FOG

Treating fats, oils, and grease can yield both environmental and economic benefits

Melissa Hamkins

Fats, oils, and grease (FOG) have a bad name in the wastewater industry. That’s largely because FOG has caused serious problems in wastewater collection systems and treatment plants nationwide. FOG can coat collection pipes and treatment equipment, restrict flow, and coat instrumentation, such as level indicators — rendering them useless. Left uncontrolled, FOG can be a major maintenance headache and lead to sewer overflows and reduced wastewater treatment efficiency.

Due to these difficulties, many municipalities have been working to develop, institute, and enforce regulations that limit the discharge of FOG to their collection systems. Local regulations have targeted the prime culprits — food-handling establishments — often mandating the use of grease traps to collect FOG. In many communities, enforcement of these rules has significantly reduced the amount of FOG discharged to their collection systems and received in their wastewater treatment plants. Read full article.

Fix It or Replace It?

A risk-based approach to making asset rehabilitation and replacement decisions

Pervaiz Anwar and Pam Koester

Water and wastewater treatment professionals typically rely on their experience and best judgment to determine how long a piece of equipment will last and then base capital investment decisions on these determinations. There may be a better way.

The Orange County (Calif.) Sanitation District (OCSD; Fountain Valley) manages wastewater for about 2.3 million residents in a 1220-km2 (470-mi2 ) area of central and northwest Orange County. The district needed to determine the condition of existing assets so staff could schedule appropriate repairs and replacements under its asset management program. As part of this effort, OCSD hired a consulting firm to assess when various equipment assets in Plant No. 2’s 11-digester complex were likely to fail, note the consequences of such failures, and recommend whether to repair or replace each asset.

To save time and money, the project team began by evaluating various modes and consequences of equipment failures and ranking how critical each asset is (to avoid making detailed assessments of noncritical equipment). The team’s results showed that this risk-based approach could substantially reduce asset life-cycle costs. Read full article.

Operations Forum Features

Add hydrogen sulfide to a reinforced concrete box conduit for 30 years, and you have a formula that has the potential to produce a catastrophic failure.

The 12-ft by 9-ft (3.7-m by 2.7-m) box conduit was put in service in the Metro Wastewater Reclamation District (Metro; Denver) South Plant in 1976 to carry primary effluent from four 150-ft-diameter (45.7-m-diameter) primary clarifiers to eight nearby aeration basins and 10 secondary clarifiers. As operated in 2005, the conduit was conveying as much as 144 mgd (545,000 m3/d) of primary effluent during peak flows.

But years of operating concept for the old, unlined box conduit at less than totally full had led to excessive hydrogen sulfide damage had eroded as much as 7 in. (178 mm) of concrete from the original 14-in.-thick (356-mm-thick) roof.

Metro acted swiftly and surely to orchestrate the massive bypass and construction project needed to rehabilitate the conduit. Read full article.

The Ultimate Public Relations Tool

Getting the Most From a Consumer Confidence Report

Esmond K. Scott

There is a general perception that the water coming from America’s tap is not pure. Water coming from other sources — particularly fancy bottles on grocery shelves — represent water that is pure and clean. That this myth has pervaded and continues is largely a result of marketing by water bottlers and a lack thereof by water utilities.

For some utilities therefore, the right-to-know provisions in the 1996 amendments to the Safe Drinking Water Act provided a golden opportunity in the form of the consumer confidence report (CCR). The Public Utilities Department of the City of North Miami Beach, Fla., chose to view the mandatory reports as an opportunity to ensure that its customers receive much needed information about their drinking water and the utility that produces it. Read full article.

Communication Is King

Effective public outreach helps ensure public support for construction of a pump station in a residential neighborhood

Craig J. Smith, Helena Galvan, and Agustin Lopez

When County Sanitation District 1 (CSD-1; Rancho Cordova, Calif.) needed to construct a new pump station and force main in Fair Oaks, Calif., a residential suburb in eastern Sacramento County, the project team was concerned about possible objections from the local community. The team particularly was concerned because the area is almost fully developed, with no vacant parcels available adjacent to the existing trunk sewer. Although a small area within a large apartment complex nearby provided an option, acquiring the land would require skill and finesse. More importantly, however, the team realized that public acceptance would be crucial to the success of the Madison Avenue Pump Station Project.

By reaching out to the community and addressing their concerns, the team succeeded in garnering support and helped ensure that no significant complaints or requests for design changes arose. During the course of the project, the team discovered that the outreach efforts provided valuable input to the project’s design and construction phases, and reduced costs. Read full article.